Variable resistor



Oct. l5, 1963 R. E. cADDocK ETAL VARIABLE REsIsToR Filed April 29, 1959N@ iw,

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United States Patent 67,335 VARABLE RESESTQE Richard E. Caddocir, Ames,iowa, and Warren D.. Heibert, Riverside, Calif., assignors to Eourns,line., a ecrporation of @alitornia Filed Apr. 2%, i959, Ser. No. tlStJlStalins. (Cl. 33h-lh) The present invention relates to variableresistors, and more particularly to precision potentiometers of the typewherein a wiper is moved along a resistance element by means of arotatable leadscrew.- One of the primary objects of the invention is toprovide a potentiometer of the class described, which is sealed againstthe entrance of humidity and dust, and which is so constructed as topermit its manufacture in extremely small sizes.

A further object of the invention is to provide a leadscrew actuatedpotentiometer having a high degree of reliability, exceptional stabilityof settings, and extreme accuracy of adjustment.

Another object is to provide a leadscrew actuated potentiometer which isextremely simple in cons-truction, and which can be quickly and easilyassembled.

Still another object of the invention is to provide a leadscrew actuatedpotentiometer capable of operating at relatively high temperature.

These objects are achieved in the present invention by a constructionembodying a housing or body of high temperature resistant plastic havinga cavity formed in one side thereof, in which a leadscrew is journaled.Mounted on the said one side of the housing is a lid holding aresistance element having a ceramic mandrel. A slider is operativelyassociated with the leadscrew and has a contact wiping on the element,the said slider forming an electrical connection between the element andthe leadscrew. Terminals are electrically connected to the leadscrew andto the resistance element, and a screw adjusting head is connected toone end of the leadscrew by a non-conductive coupling member.

The construction of the slider forms one `aspect of the invention andcomprises a U-shaped sheet metal body which engages the leadscrew frombelow and tits snugly against opposite sides thereof. A generallyU-shapcd spring wire Contact member has its ends anchored in the bottomof the slider body adjacent one end thereof, and the arms of the springWire contact member are bowed into an arc of approximately 180 degrees`and extend upward alongside the leadscrew adjacent the other end of theslider body. The center portion of the U- shaped contact member passesthrough vertical guide slots in the sides of the slider body, andextends across the top of the leadscrew, yieldingly engaging the threadof the leadscrew midway between the ends of .the slider body to providea releasable driving connection between the slider and the leadscrew.Electrical connection is made between the resistance element and theleadscrew by the Contact member, and the leadscrew is electricallyconnected, in turn, to one of the terminals by means of a spring clip ofnovel construction, having `an aperture through which one end of theleadscrew passes, and a bowed spring linger which overlies the leadscrewand presses against the same with spring pressure.

rl`he foregoing and other objects and advantages of the invention willbecome apparent to those skilled in the art upon consideration of thefollowing detailed description of a preferred embodiment thereof,reference being had to the accompanying drawings, wherein:

FIGURE 1 is a longitudinal section, taken lat i-l in FlGURE 2, through aleadscrew actuated potentiometer embodying the principles of theinvention;

FIGURE 2 is a transverse sectional view of the same taken at 2-2 ofFlGURE l;

FIGURE 3 is a sectional view, URE l; and

FIGURE 4 is an exploded perspective view of the housing land lid of theinstrument illustrated herein.

in the drawings, the instrument is designated in its entirety by thereference numeral l0, and is seen to comprise `a generally rectangularbody il of electrically nonconductive, high temperature plastic orequivalent material, having a cavity l2 formed in one side thereof, anda lid .t3 mounted on said one side to enclose said cavity. The main`portion of the cavity l2 is relatively deep, and occupies approximatelytwo-thirds of the length of the housing in the mid-portion thereof;there being a relatively shallow portion i4 of the cavity extending fromone end of the main portion l2 to the adjacent end of the body il. Thesides of the cavity are flat `and substantially parallel, except fornarrow shoulders 1.5 and le, which extend lengthwise of the body alongthe sides thereof. At the end of the body opposite the shallow portie-nit, :the cavity is provided with a step 2t), which provides support forone end of the lid 13.

Rotat-abiy supported within the body il parallel to the longitudinalthereof, is a leadscrew 2i having a smooth unthreaded portion at one endthereof. The Smooth portion 22 of the leadscrew is inserted into andjournaled within a smooth bearing hole 23. At its other end, theleadscrew 2l is enlarged in diameter to provide a smooth surfacedcylindrical portion 24, which is journaled within a bore 2.5 in the bodyil.. The enlarged cylindrical portion 2dof the leadscrew is providedwith a circumferential groove 216, which is engaged by a U- shapedretainer 3b that is seated within the housing il, to hold the leadscrewagainst endwise movement.

The enlarged portion 24 of the leadscrew terminates within the bore Z5,and is provided with a socket 3l in its end, into which is inserted oneend of a coupling member 32 of ceramic or other electricallynon-conductive material. The other end of the coupling member 32 isinserted into a socket 33 in a head 34, which is disposed within aslightly enlarged counterbore 3S in the end of the body. The outer endof the head 3ft projects beyond the end of the body il and is slotted at36 to receive a screwdriver blade. The coupling member 32 is aninterference tit in both of the sockets 3l and 33, `and thus the headTiltis fixedly connected to the leadscrew 2l so that the two rotate asone. The adjacent ends of the enlarged port-ion and head 34 are spacedapart slightly to form a circumferential groove, and disposed withinthis groove is an O-ring @il of elastomeric material, which eals theclearance between the leadscrew and the body il vagainst the entrance ofmoisture or dirt into the cavity.

The lid i3 is likewise formed of non-conductive material, and isprovided with an outer surface 41, which is ilush with the outer surfaceof the body 11 when assembled in place. One end ofthe lid 13 is providedwith a ledge 42 which seats on the step 2f?, while the other end d3 isrelatively shallow to fit within the shallow groove i4, `and is providedwith a shallow channel 44'- on its inner surface (see FIGURE 4) toforman aperture through which the terminal wires pass. Between the ledged2 and end portion 43, the lid i3 has sides 46 and 4-7, which projectdown into the cavity l2 and seat on the shoulders i5. The sides 46 and47 are connected at one end by an end wall 4S, which ts against the endof the cavity l2 and abuts against the leadscrew retainer to hold thelatter in place.

The inwardly projecting portion of the lid 13 has a narrow slot E@provided therein, with slightly enlarged end portions 5l and 52. Seatedwithin the slot 5t?, 5l, S2 is a resistance element 53, which may eitherbe of the wirewound type, as shown, or it may be a composition eletakenat 3 3 in FIG- entrasse ment. In the illustrated embodiment, wirewindings are wrapped around a ceramic mandrel dwhich is aperturedcentrally at 55 to receive a terminal strip 56. The terminal strip 56extends through the mandrel from one end thereof to the other, and atits right-hand end (FlGURE l) the strip is bent around at 57 to overlythe windings at the end of the element, where it is silver soldered orotherwise electrically connected to the resistance wire or cornposition.The left-hand end of the strip 56 projects beyond the end of the mandrel54, and is soldered or spot welded to a terminal wire 649 lying withinthe channel i4 in the lid i3. The resistance wire windings at theleft-hand end of the element are electrically connected by a tab oil tothe upturned end of a terminal wire 62, which is likewise idsposedwithin the channel ll of the lid l. The terminal wires 60 and 62 areseparated from one another by a triangularly shaped spacer 63 whichprojects upwardly from the bottom of the channel ed. Also, terminal wire62 extends upwardly through a diagonal slot 641 in the end of the bodyIll, so that the terminal wires are spaced apart where they leave theinstrument body.

When the lid "i3 is assembled to the body ll, the resistance element 53extends parallel to the leadscrew 2l and is spaced a short distancetherefrom. Associated with the leadscrew 21 and operatively connectedtherewith is` a slider 65 having a contact member 66 which wipes on thetop surface of the resistance element 53 to form an electricalconnection between the element and the leadscrew. The slider 65 ispreferably formed of sheet metal bent into a generally U-shapedconfiguration, and engages the leadscrew 2l from below. The slider 65has a bottom 70 and upwardly projecting sides 7l at opposite sidesthereof. The contact 66 includes a portion lying on top of the bottom'70, and is bent down over one end and back at an angle to provide aspring iinger having a rounded end portion i2 that wipes on theresistance element. The portion of the contact member 66 overlying thebottom 7@ is silver soldered or spot welded to the said bottom portion,and bears against the underneath side of the leadscrew, to makeelectrical contact therewith. The sides 7l of the slider t snuglyagainst opposite sides of the leadscrew 2l, as shown in FIGURE 2, andformed in the top edges of the sides are vertical guide slots 73, thepurpose of which will be explained presently.

The driving connection between the leadscrew 2l and slider 65 iseffected by means of a spring wire member 'ld which is bent into agenerally U-shaped conguration, with its ends projecting up into holesin the bottom 70 of the slider, where they are soldered or otherwiserigidly joined to the bottom 70. As best shown in FIG- URE l, the sidesof the spring wire member extend downwardly and to the right from theirpoint of attachment, and then extend upwardly and rearwardly in anarcuate bow along both sides of the leadscrew to the point where theyjoin the center section 74' that extends transversely across the top ofthe leadscrew. This transverse center portion 74 of the spring wireextends through and is slidable vertically within the guide slots '73,so that its movement is restricted by the slots. The center portion 74of the spring wire member yieldingly engages the thread of theleadscrew, so that as the leadscrew is turned, the slider 65 is movedlengthwise thereof.

Being free to move vertically within the guide slots 73, the centerportion '74 of the spring wire member 74 is adapted to ride up over thecrests of the leadscrew threads when the leadscrew is forcibly turnedwhile the slider is restrained against free movement lengthwise of theleadscrew, as when the slider has reached either end of its travel. Thelong length of spring arm afforded by the bowed side portions of thespring member "/4 provides a considerable amount of resiliency, allowingthe center portion 74 to ratchet over a turn of the leadscrew threadwithout unduly stressing the sides of the spring wire member. It willalso be noted that the spring wire member '74 engages the leadscrewthread approximately half way between the ends of the slider 65. rlhisis an important feature, as it tends to stabilize the slider by holdingboth ends of the bottom 7d firmly against the bottom of the leadscrew.The slider is thus prevented from becoming cocked at an angle to theleadscrew, as might otherwise happen if the spring wire member engagedthe leadscrew adjacent one end oi the slider. Tabs iii) are bentdownwardly from opposite sides of the bottom '7d of the slider adjacentone end thereof, and these tabs Si) slidably engage the sides of thebody lll, as shown in FIGURE 2, so as to restrain the slider againstttirningv'ith the leadscrew.

Those skilled in the art will recognize from the foregoing descriptionthat the leadscrew 2l serves as an electrical return from the contact66. The leadscrew is adapted to be connected into the electrical circuitwith which the potentiometer l@ is to be used, by means of a terminalwire 8l which extends through a hole 32 in the end of the body lll. Theterminal wire 8l projects into the cavity l2 and through an aperture 83in a leadscrew terminal clip 84, which bears against one end of thecavity l2. The terminal clip S4 is also provided with a circularaperture S5 through which the smooth bearing portion 22 of the leadscrew2l passes. Flanges 86 are bent inwardly from the side edges of the clip84, and these anges bear against the sides of the cavity 12 to hold theclip against lateral displacement. Bent downwardly from the top edge ofthe clip 8d is a bowed spring tnger 87, the free end of which yieldinglypresses against the smooth bearing portion 22 of the leadscrew to makeelectrical contact therewith. The terminal wire 3l lies against one ofthe side flanges 86 and is silver soldered or otherwise suitably joinedthereto.

The potentiometer 10 is adapted to be mounted upon a suitable supportingstructure, and to this end the body 1l is provided with a pair ofmounting holes 9i) adjacent the ends of the body. Mounting screws may bepassed through the holes 9h to secure the body lll to the supportingstructure. Y

In assembling the potentiometer 1l), the leadscrew 2l Vwith the head 34and coupling member 32 assembled thereto is inserted through the bore25, and the slider 65 is slipped over the inner end of the leadscrew sothat the spring wire member 74 is operatively engaged with the threadsof the leadscrew. The smooth bearing portion 22 of the leadscrew is theninserted through the hole in the terminal clip 34, and into the bearinghole 23. When the leadscrew 21 is fully seated in the body 1l, theretainer 3i) is slipped down into the cavity 12 so that it engages thecircumferential groove 26 in the large bearing portion 24 at the headend of the leadscrew. The resistance element 53, with terminal wires 6l)and 62 attached thereto, is then inserted into the cavity 5t), 5l, 52 inthe lid i3, and the lid is dropped into place in the open side of thebody 11, so that it closes the cavity l2. The lid 13 is cemented to thebody around its entire edge, and the apertures in the end of the bodythrough which the terminal wires 60, 62 and S1 pass are then lled with asuitable potting agent, such as epoxy resin 95. The instrument is thenready for use.

While we have shown in considerable detail what We believe to be thepreferred form of our invention, it will be understood by those skilledin the art that various changes may be made in the shape and arrangementof the several parts without departing from the scope of the followingclaims.

We claim:

1. A variable resistor comprising an elongated body having a cavityformed in one side thereof, a lid mounted on said one side of said bodyof enclose said` cavity, a resistance element mounted on the inner faceof said lid and having a pair of terminal wires connected to the endsthereof, said lid having one end portion thereof projecting -to the endof said body, said projecting one end portion being received within ashallow groove in said one side of said body and cooperating therewithto form an aperture through which said terminal wires pass, a leadscrewrotatably supported on said body within said cavity parallel to saidresistance element, a slider operatively engaged by said leadscrew ltobe moved thereby, said slider having a contact wiping on said resistanceelement and Ielectrically connected to said leadscrew, and a thirdterrninal wire electrically connected to said leadscrew.

2. A variable resistor comprising a body, a resistance element mountedon said body, `a leadscrew of conductive material disposed parallel tosaid resistance element and rotatably supported at its ends by saidbody, said leadlscrew having fa smooth unthreaded portion adjacent oneend thereof, Aa slider operatively engaged by said :leadscrew so as Itobe moved thereby when the Ileadscrew is turned, contact means yon saidslider wiping on said resistance element and making electricalconnection with said leadscrew, la lea-dscrew terminal clip ofconductive sheet metal comprising a rst part perpendicular to the axisof said leadscrew and a second part perpendicular to said first part,said first part having an aperture provided therein through which saidsmooth portion `of said leadscrew extends, said second part having a lipat its outer end yieldingly engaging said smooth portion of saidleadscrew to make electrical contact therewith, and terminal meansconnected to said clip.

3. A variable resistor comprising an elongated body having a cavityformed in one side thereof, an electrically conductive leadscrewextending through said cavity and journaled at its ends in the ends ofsaid body, said leadscrew having a smooth Unthreaded portion adjacentone end thereof, a lid mounted on said one side of said body to enclosesaid cavity, a resistance element mounted on the inner face of said lidparallel to said leadscrew, a slider operatively engaged by saidleadscrew so as to be moved thereby when the leadscrew is turned,Contact means on said slider wiping on said resistance element andmaking electrical connection with said leadscr'ew, a leadscrew terminalclip of conductive sheet metal, said clip havng la center portondisposed perpendicular to the longitudinal axis of said ieadscrew, andside portions bent at right angles yto said center portion so as to lieflat against the side walls of said cavity, said center portion havingyan aperture provided therein through which said smooth portion of saidleadscrew passes, a top portion bent at right angles to said centerportion so` as to overlie said leadscrew, said top portion 'having -alip yieldingly engaging said smooth portion of said leadscrew to makeelectrical contact therewith, and terminal means connected to said clip.

4. In a variable resistor having a housing, a leadscrew rotatablysupported on said housing, and a resistance element mounted on saidhousing parallel to said leadscrew, the improvement comprising a sliderconsisting of a generally U-shaped sheet metal body, the bottom of saidU-shaped slider body bearing against the bottom of said leadscrew andthe sides -thereof extending upwardly along opposite sides of theleadscrew, said sides having generally vertical guide slots formed inthe top edges thereof adjacent the midpoint of said body, `a spring wiremember bent into a generally U-shaped configuration, the ends of saidspring wire member being anchored in the bottom of said slider bodyadjacent one end thereof, the arms of said spring wire member beingbowed and extending upwardly alongside said leadscrew adjacent the otherend of said slider body, the center portion of said spring wire memberextending transversely across the top of said leadscrew and yieldinglyengaging the thread thereof, said center portion of said spring memberbeing slidable vertically within said guide slots to allow the same toride up `over .-the crests of the leadscrew thread when said leadscrewis forcibly turned while said slider is restrained against free movementlengthwise of the leadscrew, 'and a contact member attached #to thebottom of said slider body and wiping on said lresistance element.

5. The invention as deiined in claim 4, wherein said slider body hasltabs bent downwardly from the bottom thereof adjacent the sides, saidtabs slidably engaging the sides of said housing so as to prevent saidslider body from turning with said leadscrew.

References Cited in the file of this patent UNITED STATES PATENTS2,745,054 Leyenberger May 8, 1956 2,860,216` Hubbard Nov. 1l, 19582,870,302 Bourns Jan. 20, 1959 2,870,304 OBrian Jan. 20, 1959 2,873,337Bourns Feb. 10, 1959 2,873,338 Elliott Feb. 10, 1959 2,882,375 BournsApr. 14, 1959 2,886,681 Bourns May 12, 1959 2,895,116 Morrison July 14,1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,1075336 October l59 1963,

Richard E. Caddock et al.,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4', line 69, for "of enclose read to enclose column 5, line 39,for "porton" vread --M portion Signed and sealed this 21st day of April1964a (SEAL) Attest: EDI/JARD J. BRENNER ERNEST W. SWIDER AttestngOfficer Commissioner of Patents

1. A VARIABLE RESISTOR COMPRISING AN ELONGATED BODY HAVING A CAVITYFORMED IN ONE SIDE THEREOF, A LID MOUNTED ON SAID ONE SIDE OF SAID BODYOF ENCLOSE SAID CAVITY, A RESISTANCE ELEMENT MOUNTED ON THE INNER FACEOF SAID LID AND HAVING A PAIR OF TERMINAL WIRES CONNECTED TO THE ENDSTHEREOF, SAID LID HAVING ONE END PORTION THEREOF PROJECTING THE END OFSAID BODY, AND PROJECTING ONE END PORTION BEING RECEIVED WITHIN ASHALLOW GROOVE IN SAID ONE SIDE OF SAID BODY AND COOPERATING THEREWITHTO FORM AN APERTURE THROUGH WHICH SAID TERMINAL WIRES PASS, A LEADSCREWROTATABLY SUPPORTED ON SAID BODY WITHIN SAID CAVITY PARALLEL TO SAIDRESISTANCE ELEMENT, A SLIDER OPERATIVELY ENGAGED BY SAID LEADSCREW TO BEMOVED THEREBY, SAID SLIDER HAVING A CONTACT WIPING ON SAID RESISTANCEELEMENT AND ELECTRICALLY CONNECTED TO SAID LEADSCREW, AND A THIRDTERMINAL WIRE ELECTRICALLY CONNECTED TO SAID LEADSCREW.